1.1 Technical Field
The invention relates to a process for depositing at least one thread or tape, generally a metal thread or tape, on a thin sheet, especially a plastic, paper or aluminum sheet, this sheet being able to be joined to another sheet with the thread or tape sandwiched between them, the sheet furnished with the thread or tape subsequently being wound up into a reel, in particular for transportation and/or storage.
The invention relates more particularly, but not exclusively, to the deposition of a metal thread or tape made of magnetic material having a high permeability for a system for protecting against the theft of articles in stores.
1.2 Description of Related Art
Thin sheets or films of plastic, paper, aluminum or other material, furnished with a metal thread or tape, in particular a magnetic one, are being increasingly used either for the closure of containers containing products or for the manufacture of labels affixed to the products, so as to be able to provide, by virtue of the presence of the metal thread or tape, information on the product or antitheft protection, by detecting the metal thread or tape with a suitable system.
Examples of devices enabling articles to be detected using such magnetic metal threads or tapes are provided, inter alia, by EP-A-0,130,286, EP-A-0,295,028 or WO 92/07343. The metal thread or tape is made of a magnetic material having a high permeability, for example an alloy known by the name "permalloy".
The thickness of the metal thread or tape placed on the sheet of plastic or other material is relatively small, but nevertheless constitutes an additional thickness which is added to the thickness, also relatively small, of the sheets between which this thread or tape is sandwiched.
The sheets thus equipped are manufactured in long length, for example a length of several tens of meters, and are wound up into reels for storage and/or transportation, these sheets subsequently being cut into individual sheets, for example to make lids for containers or labels, depending on the application envisaged.
The reels of sheet thus formed have a relatively large number of turns. Under these conditions, if the metal thread or tape is arranged parallel to the length of the sheet (see FIG. 1a) while the latter is being wound up about an axis orthogonal to its length, the additional thicknesses of the thread or tape come to be superimposed in the wound reel (see FIG. 1b) and to create a protuberance possibly resulting in deformations which can damage the sheets to which a metal thread or tape is fixed.